Serious ducks diagnostic problem 2000 Cavalier 2.2L

OK.
2000 Cavalier w/ 90000 miles. Low reservoir light came on... ended up replacing
thermostat. Had HUGE ISSUES bleeding it & actually put 112 miles on it before it
overheated AGAIN. Also have new coolant temp sensor and coolant reservoir....AND a
new fan, that does kick on properly
It continues to do the following every 100 or so miles:
Will leave house/work w/ car completely full of coolant, heat blowing very hot,  a/c works
great... then all of a sudden the low reservoir light will come on for 3-4 seconds (MAX)
then blow out all the coolant. Temp gauge NEVER climbs passed 195 and I've yet to be
able to pull over fast enough to figure out from where the coolant is letaking,  but  its
always empty by the time I do. (I usually pull over within 60 to 90 seconds ;-)

Also, when I've bled it lately, unless I've got significant pressure going INTO coolant
reservoir from hose many times nothing comes outta the bleed valve... Even if I've bled it
for a hour or so using the garden hose on med power... I've put in vinegar (assuming it had
clots of rust/calcium/lime....

I am DESPERATE for some help here...... if anyone can help me figure this out,  I'd be a
very happy girl!  Z
Please note * I'm nearly an expert on this particular cavaliver,  lol....